One process presently used in retreading tires requires that they be buffed to remove the old tread, then provided with a predetermined layer of uncured rubber and finally placed in an appropriately dimensioned matrix with the uncured rubber then cured at a predetermined temperature for a predetermined time.
In this process, the uncured rubber is applied by a so-called extruder builder having a section provided with a rotatable support for a buffed tire which support is expansible to center and seal the tire with the tire then automatically inflated. A ribbon-like extrusion of uncured rubber is then applied to the tire while it is so rotated and the section so turned on a vertical axis that the buffed area is covered from side-to-side with overlapping turns of uncured rubber until the tire is built up with a wanted thickness thereof. The extrusion may, for example, be one and one-eighth inches wide and three-sixteenths of an inch in thickness but the extruder builder permits adjustments as to both dimensions. Extruder builders are operated on a programmed basis, each program relating tire size to a matrix of particular dimensions and providing for the addition to the tire of a predetermined thickness of uncured rubber.
By way of example, it may be required, when one particumatrix is to be used, that a buffed tire of appropriate size be built up with uncured rubber to a thickness of 11/32nds of an inch but if a winter tread is to be formed, using another matrix, the required built up thickness for that tire would be 14/32nds of an inch.
The problem is that the diameter of buffed tires of the same size may vary and the layer of uncured rubber must be of a predetermined minimum thickness. The matrix for use with tires of one size is fixed so that in the retreading of a group of buffed tires of the same size, there may be some that should not be used as well as some that may require additional uncured rubber. This problem has been recognized and it has been the practice to measure the circumference of uninflated tires and also to take transverse measurements from bead-to-bead to determine whether and under what conditions, a buffed tire can be retreaded.